Deltamethrin-Induced Respiratory and Behavioral Effects and Adverse Outcome Pathways (AOP) in Short-Term Exposed Mozambique Tilapia, Oreochromis mossambicus

Abstract

Disrupted behavior and respiratory distress effects of 96-h acute deltamethrin exposures in adult Mozambique tilapia, Oreochromis mossambicus, were investigated using behavioral indices and opercular movement, respectively. Deltamethrin concentrations were found to be associated with toxicological (lethal and sublethal) responses. At 24, 48, 72, and 96 h, the LC50 values and 95% confidence limits were 12.290 (11.174-14.411 µg/L), 12.671 (11.334-15.649 µg/L), 10.172 (9.310-11.193 µg/L), and 8.639 (7.860-9.417 µg/L), respectively. The GUTS-model analysis showed that GUTS-SD (stochastic death) with a narrow tolerance distribution in deltamethrin exposed O. mossambicus populations was more sensitive than the GUTS-IT (individual tolerance) model. Prior to death, exposed fish demonstrated concentration-dependent mortality and disturbed behavioral responses, including uncoordinated swim motions, increased mucus secretion, unbalanced and unpredictable swimming patterns, and inactivity. The altered behavioral patterns and increased opercular movement with increased deltamethrin levels and exposure time are strongly suggestive of neurotoxicity and respiratory distress, respectively. Adverse Outcome Pathways (AOPs), describing biological mechanisms and plausible pathways, highlighted oxidative stress and cholinergic effects as intermediate steps linked to respiratory distress and behavioral toxicity.

Keywords: behavioral toxicity; in silico analysis; neurotoxicity; respiratory distress; structural homology.

Figure 1

(a) Figure 1. NOEC and LOEC (after 24 h); MATC and LC₅₀ value (after 96 h) for O. mossambicus exposed to deltamethrin. (b) Kaplan–Meier survival curves of O. mossambicus exposed to various exposure concentrations of deltamethrin (log-rank (Mantel-Cox) test: Chi square-88.14; df 10; p value: < 0.0001).

Figure 2

Relative fit of observed and fitted values of the (a) GUTS-SD and (b) IT models at different deltamethrin exposure concentrations.

Figure 3

Mean oxygen consumption of O. mossambicus (mg/h/g wet body weight/L) exposed to various exposure concentrations of deltamethrin during various exposure periods. Asterix indicates significant differences in mean parameters (p < 0.05) across exposure intervals for each concentration.

Figure 4

Changes of behavioral parameters (a) mucous secretion, (b) erratic swimming behavior, and (c) loss of balance behavior in O. mossambicus exposed to different concentrations of deltamethrin. Asterix indicates significant differences in mean parameters (p < 0.05) across exposure intervals for each concentration.

Figure 4

Changes of behavioral parameters (a) mucous secretion, (b) erratic swimming behavior, and (c) loss of balance behavior in O. mossambicus exposed to different concentrations of deltamethrin. Asterix indicates significant differences in mean parameters (p < 0.05) across exposure intervals for each concentration.

Figure 5

Correlation plot between deltamethrin concentration (CoDltm), mortality percentage (MOR%), and behavioral biomarkers; i.e., erratic swimming (ES), mucous secretion (MS), movement (M), erratic swimming (ES), loss of balance (LoB), and oxygen consumption (OC) for O. mossambicus.

Figure 6

The equivalents to deltamethrin based on the Morgan fingerprints, (a) displays the eight closest analogues of deltamethrin. The analogues are shown in a clockwise manner and in declining order of Jaccard similarity, which is indicated by a red highlight (as decimal numbers followed by ‘c’). Where unnamed, chemical (chemical without trade name) = (S)-Cyano(3-phenoxyphenyl) methyl (1R,3S)-2,2-dimethyl-3-(1,2,2,2-tetrabromoethyl) cyclopropane-1-carboxylate. (b) Common substructure denoted highlighted in red shade.

Figure 7

AOP for (a) respiratory impairment and (b) behavioral toxicity by deltamethrin in O. mossambicus. The boxes represent toxic responses documented in aquatic species, including O. mossambicus exposed to deltamethrin. Arrows denote postulated Key Event Relationships (KER).